Aerodynamic drag reduction system

ABSTRACT

Provided is an aerodynamic drag reduction apparatus for reducing aerodynamic drag on an over-the-road vehicle while underway. The aerodynamic drag reduction system includes a frame assembly that is adapted to cooperate with a cargo-carrying portion of the over-the-road vehicle to couple the drag reduction apparatus to the over-the-road vehicle. First and second skirts are adapted to be supported beneath opposite lateral sides of the cargo-carrying portion of the over-the-road vehicle by arcuate rails. The first and second skirts are coupled to the frame assembly in a manner that allows thermal expansion and contraction of the first and second skirts relative to the frame assembly without warping of material forming an air-deflecting surface of the first and second skirts to an extent that would otherwise occur if the first and second skirts were fixedly connected to the frame assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior application Ser. No.13/675,205, filed Nov. 13, 2012, which claims the benefit of U.S.Provisional Application No. 61/557,967, filed Nov. 10, 2011, which isincorporated in its entirety herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates generally to the reduction of aerodynamic dragexperienced by a vehicle and, more specifically, to a system formanaging the flow of air about a portion of an over-the-road vehicle toreduce the aerodynamic drag experienced by such a vehicle while underwayand improve fuel economy.

2. Description of Related Art

Over-the-road vehicles such as a semi-truck, box truck, intermodalfreight vehicle, and other commercial vehicles typically include atractor that tows a trailer or otherwise transports a cargo hauler. Thetractor is a large vehicle engineered for towing power and durability.As such, conventional tractors typically have a large surface area onwhich drag forces act while the tractor is underway, causing the tractorto experience poor fuel economy, which contributes significantly to thecost of transporting freight from one location to another.

The fuel economy of the tractor further affected by aerodynamic drag isworsened when towing a trailer or otherwise transporting cargo. The rearwheels and suspension assembly of commercial vehicles, which can belocated adjacent to a tail end of a trailer are often spaced far enoughapart from the tractor that air can enter the space beneath the trailerfrom each side. This air contacts the rear wheels and suspension systemand further contributes to the overall aerodynamic drag experienced bythe vehicle.

BRIEF SUMMARY OF THE INVENTION

According to one aspect, the subject application involves an aerodynamicdrag reduction apparatus for reducing aerodynamic drag on anover-the-road vehicle while underway. The aerodynamic drag reductionsystem includes a frame assembly that is adapted to cooperate with acargo-carrying portion of the over-the-road vehicle to couple the dragreduction apparatus to the over-the-road vehicle. A first skirt isadapted to be supported beneath a first lateral side of thecargo-carrying portion of the over-the-road vehicle, and a first upperrail is provided to be coupled adjacent to an upper region of the firstskirt. The first upper rail extends longitudinally along the first skirtand provides the first skirt with an arcuate region between forward andtrailing regions of the first skirt. The arcuate region can optionallyextend the entire length of the first skirt. Similarly, a first lowerrail is provided to be coupled to the first skirt at a verticalelevation between the first upper rail and a bottom region of the firstskirt. Like the first upper rail, the first lower rail extendslongitudinally along the first skirt.

A second skirt is adapted to be supported beneath a second lateral side,opposite the first lateral side, of the cargo-carrying portion of theover-the-road vehicle. Similar to the first upper rail, a second upperrail that is provided to be coupled adjacent to an upper region of thesecond skirt to extend longitudinally along the second skirt andestablish an arcuate region along the second skirt between forward andtrailing regions. A second lower rail is provided to be coupled to thesecond skirt at a vertical elevation between the second upper rail and abottom region of the second skirt, also to extend longitudinally alongthe second skirt.

According to another aspect, the subject application involves anaerodynamic drag reduction apparatus for reducing aerodynamic drag on anover-the-road vehicle while underway. The aerodynamic drag reductionsystem of the present aspect includes a frame assembly that is adaptedto cooperate with a cargo-carrying portion of the over-the-road vehicleto couple the drag reduction apparatus to the over-the-road vehicle. Afirst skirt is provided and adapted to be supported beneath a firstlateral side of the cargo-carrying portion of the over-the-road vehicle.A second skirt is also provided, and is adapted to be supported beneatha second lateral side, opposite the first lateral side, of thecargo-carrying portion of the over-the-road vehicle. The spacing of thefirst and second skirts establishes a space separating a leading portionof the first and second skirts. A coupling system is provided to couplethe first and second skirts to the frame assembly in a manner thatallows thermal expansion and contraction of the first and second skirtsrelative to the frame assembly without warping of material forming anair-deflecting surface of the first and second skirts to an extent thatwould otherwise occur if the first and second skirts were fixedlyconnected to the frame assembly.

The above summary presents a simplified summary in order to provide abasic understanding of some aspects of the systems and/or methodsdiscussed herein. This summary is not an extensive overview of thesystems and/or methods discussed herein. It is not intended to identifykey/critical elements or to delineate the scope of such systems and/ormethods. Its sole purpose is to present some concepts in a simplifiedform as a prelude to the more detailed description that is presentedlater.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention may take physical form in certain parts and arrangement ofparts, embodiments of which will be described in detail in thisspecification and illustrated in the accompanying drawings which form apart hereof and wherein:

FIG. 1 shows a perspective view of an illustrative embodiment of acommercial truck comprising a tractor and a trailer to which an air dragreduction system has been coupled;

FIG. 2 is a side view of an illustrative embodiment of a trailer towhich an air drag reduction system has been coupled;

FIG. 3 is a bottom view of the trailer shown in FIG. 2;

FIG. 4 is a bottom view of an illustrative embodiment of an intermodaltrailer to which an air drag reduction system has been coupled;

FIG. 5 is a cross-sectional view of a portion of the intermodal trailertaken along line 5-5 in FIG. 4, wherein a frame member of an air dragreduction system is shown resting atop structural beams of theintermodal trailer;

FIG. 6 is a cross sectional view of the structural beams of theintermodal trailer shown in FIG. 4 with an alternate illustrativeembodiment of a frame member of an air drag reduction system coupled tothe structural beams;

FIG. 7 a is a cross-sectional view of a portion of the trailer takenalong line 7-7 in FIG. 3, showing an illustrative embodiment of acoupling mechanism aligned for installation of an air drag reductionsystem on an underside of a trailer;

FIG. 7 b is a cross-sectional view of a portion of the trailer takenalong line 7-7 in FIG. 3, showing the coupling mechanism installed onthe underside of the trailer;

FIG. 8 is a perspective view of an illustrative embodiment of a skirtsegment coupled to top and bottom rails that form a portion of a frameassembly for coupling an air drag reduction system to an underside of atrailer;

FIG. 9 is a plan view of a skirt segment adjustably coupled to top andbottom rails forming a portion of a frame assembly for coupling an airdrag reduction system to an underside of a trailer, wherein the skirtsegment is coupled to the rails in a manner that allows the skirtmaterial to expand and contract along a longitudinal axis relative tothe rails without deformation of the skirt material that would otherwiseresult from expansion and contraction of the skirt material with a fixedcoupling;

FIG. 10 a is a cross-sectional view, taken along line 10-10 in FIG. 9,of the skirt that is to be coupled to a trailer for deflecting at leasta portion of an airflow directed toward a portion of an underside of thetrailer, wherein the skirt includes an integrally formed rib to enhancestructural rigidity of the skirt;

FIG. 10 b is a cross-sectional view, taken along line 10-10 in FIG. 9,of the skirt that is to be coupled to a trailer for deflecting at leasta portion of an airflow directed toward a portion of an underside of thetrailer, wherein the cross section of the skirt is somewhat triangularin shape to provide added rigidity adjacent to a bottom portion of theskirt;

FIG. 10 c is a cross-sectional view, taken along line 10-10 in FIG. 9,of the skirt that is to be coupled to a trailer for deflecting at leasta portion of an airflow directed toward a portion of an underside of thetrailer, wherein the cross section of the skirt is somewhat triangularin shape to provide added rigidity adjacent to a top portion of theskirt;

FIG. 11 shows an illustrative embodiment of an arrangement of a skirtprovided to an air drag reduction system, wherein an aft portion of theskirt is substantially parallel with a longitudinal axis of a trailer towhich the air drag reduction system is coupled to establish a desiredairflow relative to the trailer;

FIG. 12 shows another arrangement of a skirt relative to a trailer thatprojects a deflected portion of an airflow in a substantially transversedirection relative to a longitudinal axis of the trailer to which theair drag reduction system is coupled, which is believed to promoteturbulence adjacent to an aft portion of the trailer;

FIG. 13 is an end view of a top rail within a c-shaped bracket;

FIG. 14 is a top view of a c-shaped bracket joining ends of a top railprovided to adjoining skirt segments;

FIG. 15 shows an alternate embodiment of a joining apparatus for joiningends of a top rail provided to adjacent skirt segments; and

FIG. 16 shows the portions of the top rail coupled together with thejoining apparatus of FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used herein for convenience only and is not to betaken as a limitation on the present invention. Relative language usedherein is best understood with reference to the drawings, in which likenumerals are used to identify like or similar items. Further, in thedrawings, certain features may be shown in somewhat schematic form.

It is also to be noted that the phrase “at least one of”, if usedherein, followed by a plurality of members herein means one of themembers, or a combination of more than one of the members. For example,the phrase “at least one of a first widget and a second widget” means inthe present application: the first widget, the second widget, or thefirst widget and the second widget. Likewise, “at least one of a firstwidget, a second widget and a third widget” means in the presentapplication: the first widget, the second widget, the third widget, thefirst widget and the second widget, the first widget and the thirdwidget, the second widget and the third widget, or the first widget andthe second widget and the third widget.

FIG. 1 shows an illustrative embodiment of a truck 7 comprising atractor 14 operatively connected to a trailer 10 that is to be towed bythe tractor 14. The embodiment of the trailer 10 appearing in FIG. 1 hasa box-like enclosure 12 that is approximately 53 ft. in length in whichcargo is placed to be transported from one location to another. Supportfor the trailer's floor is provided by structural beams 35 (FIGS. 2 and3) that extend laterally, and substantially perpendicular to alongitudinal axis 32 of the trailer 10, between metallic frame members34 that extend lengthwise along the lateral sides the trailer 10 and arecoupled to opposite ends of the structural beams 35. Although theembodiment of the trailer 10 in FIG. 1 is described as a 53 ft. enclosedtrailer for the sake of brevity, it is understood that the trailer 10can be any cargo hauling platform, such a trailer attached to a commonchassis with the tractor (commonly referred to as a box truck), atrailer with an intermodal chassis as shown in FIGS. 4-6, or any othercargo-hauling trailer used in the commercial transportation of goods.

An air drag reduction system 20 is shown coupled to an underside of thetrailer 10 in FIG. 1. The air drag reduction system 20 includes a skirt22 that extends longitudinally along at least a portion of the trailer10. The skirt 22 deflects a portion of the airflow entering the spacebetween the underside of the trailer 10 and the road surface 24 whilethe truck 7 is underway. At least a portion of the deflected airflowwould otherwise impinge on the rearward tire assembly 26 supporting theaft portion 28 of the trailer 10 above the road surface 24 if notdeflected. Deflected by the skirt 22, the deflected portion of theairflow is directed laterally-outward, beyond externally-exposed sidesof the rearward wheel assembly 26, and passes by the trailer 10 in adirection substantially parallel with the trailer 10 as illustrated inFIG. 11, for example.

As shown in FIG. 2, the length L of the skirt 22, when followed alongits curvature, is approximately 20 ft., ±6 inches. The skirt 22 canoptionally also include a radius of curvature that is at least 12inches, or much larger such as at least 100 ft., and optionally about120 ft. According to alternate embodiments, the radius of curvature canbe substantially constant over the entire length of the skirt 22.However, the length L of the skirt 22 can be any desired length thatallows the skirt 22 to be installed between a leading surface of theforward-most tire 36 of the rearward wheel assembly 26 and the leadingsurface 38 of the trailer 10. Other embodiments of the skirt 22 can beapproximately 16 ft. in length, formed from four skirt segments that areeach approximately 4 ft. in length. It follows that the skirtsapproximately 20 ft. long can be formed from five skirt segments, eachapproximately 4 ft. in length. According to alternate embodiments, thelength L of the skirt 22 can be sufficient to allow the skirt 22 toextend along the longitudinal axis 30 about 15 ft. to about 21 ft., witha leading portion 42 of the skirt 22 being recessed inwardly to extendunder the trailer 10, toward a central region of the trailer 10 as shownin FIG. 3. Thus, the leading portions 42 of the skirts 22 arranged alongopposite lateral sides of the trailer 10 are closer to each other thanother portions of the skirts 22, such as trailing portions 40 forexample, while the air drag reduction system 20 is installed on thetrailer 10. Accordingly, a distance separating the leading portions 42of the skirts 22 is greater than a distance separating the trailingportions 40. Yet other embodiments call for the skirt 22 to extendapproximately 16 ft. along the axis 30, or approximately 20 ft. alongthe axis 30. Yet other embodiments include a skirt 22 sized to extend adesired portion along the axis 30 relative to the length of the trailer10 (i.e., the distance between the leading surface 38 and the aftportion 28 of the trailer 10). For instance, according to an embodimentwhere the trailer 10 is approximately 53 ft. in length, the skirt 22 canbe installed to extend approximately 20 ft., ±6 inches, along the axis30. For shorter trailers, such as those that are approximately 40 ft. inlength, the skirt 22 can have a length of about 16 ft. followed alongits curvature.

The skirt 22 can also be sized and installed on the trailer 10 toterminate at a trailing portion 40 that is separated a distance Y aheadof the leading surface of the forward-most tire 36. The distance Y aheadof the leading surface of the forward-most tire 36 allows a portion ofthe airflow deflected laterally outward from under the trailer tobeginning moving in a laterally inward direction, generally towards thespace under the trailer 10. As the portion of the deflected airflowbegins to move in the laterally inward direct, it can contribute to theaerodynamic drag exerted on the trailer 10. Since the skirt 22 includesan aft region 144 (described below with reference to FIG. 11) thatterminates with a portion of the skirt 22 substantially parallel with anexternal side of the trailer 10, the skirt 22 delays, but does notovershoot, the return of the deflected portion of the airflow in thelaterally-inward direction until after the deflected airflow is beyondthe rearward wheel assembly 26. It is believed the trailer 10experiences improved slipstream performance due to the minimization ofturbulent eddy formation behind the trailer. In other words, it isbelieved that the portion of the airflow deflected by the skirts 22passes the externally exposed sides of the rearward wheel assembly 26 ina bulk flow direction that is substantially parallel with the side ofthe trailer 10. The distance Y that the trailing portion 40 is ahead ofthe forward-most tire 36 is about 12 inches to about 24 inches.According to another embodiment, the trailing portion 40 is ahead of theleading surface of the forward-most tire 36 along the axis 30 byapproximately 18 inches while the rearward wheel assembly 26 is in theso called “California position”. The position of the rearward wheelassembly 26 can be adjusted along the longitudinal axis 30 relative tothe box-like enclosure 12, the structural beams 35 and other stationarycomponents of the trailer 10. In the California position, for a tandemaxle rearward wheel assembly 26, the rearward wheel assembly 26 isadjusted to position the centerline of the rearmost axle at a locationapproximately 146 inches, ±3.0 inches, forward along the longitudinalaxis 30 from the aft portion 28 of the trailer 10.

Likewise, the leading portion 42 of the skirt 22, which is locatedupstream of the trailing portion 40 in the airflow while the truck 7 isunderway, can be set back a distance X from the leading surface 38 ofthe trailer 10. For example, the leading portion 42 can be set back adistance X of at least about 12 ft., or optionally about 16 ft. to about20 ft. from the leading surface 38 of the trailer 10. Other embodimentscall for the leading portion 42 to be set back a distance X of about 16ft., 2 in. from the leading surface 38 of the trailer 10 to allow forthe portion of deflected airflow to again travel in a laterally inwarddirection after passing the rearward wheel assembly 26.

As shown in FIG. 3, the underside of the trailer 10 includes the exposedlaterally-oriented structural beams 35. A frame assembly 44 of the airdrag reduction system 20 couples the skirt 22 to the structural beams35. For the embodiment shown in FIG. 3, the frame assembly 44 includescross members 46 that extend between the top rails 48 a (FIG. 8)supporting the skirt 22 on each side the air drag reduction system 20.Two sets of cross members 46 are shown in the embodiment appearing inFIG. 3, with each set including a pair of cross members 46. At least onecross member 46 from at least one of the sets can be adjustably coupledto the top rails 48 a to allow that cross member 46 to be adjustedforward and rearward directions along axis 30 when the air dragreduction system 20 is supported in position under the trailer 10 forinstallation. For example, the adjustable cross member 46 can optionallybe supported on a track coupled to the stationary cross member 46 in thesame set, allowing for adjustment of the adjustable cross memberrelative to the other cross member 46. According to alternateembodiments, a receiver portion forming part of a fastening system 47described below can be adjustably coupled to one of the cross members 46in a manner that allows the receiver portion to be adjusted fore and aftalong the longitudinal axis 30 relative to the other cross member 46.Regardless of the implementation, a distance between the receiverportion and a locking mechanism allows the fastening system to cooperatewith structural beams 35 or other structural features of the trailer 10having different sizes, and thereby couple the drag reduction system 20to the trailer 10.

One or more of the cross members 46 can be provided with a fasteningsystem 47, an example of which is illustrated in FIGS. 7 a and 7 b, tosecure the frame assembly 44 to the structural beams 35 or other portionof the underside of the trailer 10. FIGS. 7 a and 7 b arecross-sectional views of a pair of cross members 46 and one of thestructural beams 35 taken along line 7-7 in FIG. 3 to illustrate amethod of coupling and removing the frame assembly 44 to and from thetrailer 10. However, each of the pairs of cross members 46 appearing inFIG. 3 can optionally be provided with the fastening system such as thatdescribed in FIGS. 7 a and 7 b. The fastening system in FIG. 7 aincludes a catch portion 50 that, along with the cross member 46,defines a generally C-shaped recess 52 that can receive a flange portion62 of the structural beam 35. The other cross member 46 in FIG. 7 asupports a hinge 54 that pivotally couples a clamp 56 to the crossmember 46. The clamp 56 is located adjacent to a locking device 60,which can also be supported by the cross member 46, that is operable tomaintain the clamp 56 in a closed orientation to interfere with openingof the clamp 56 and removal of the frame assembly 44 from the structuralbeam 35 or other portion of the trailer 10. According to theillustrative embodiment shown in FIGS. 7 a and 7 b, the locking device60 includes a threaded member 64 that can receive a locking nut 58threaded to be compatible with the threaded member 64.

To install the frame assembly 44 using the embodiment of the fasteningsystem 47 shown in FIGS. 7 a and 7 b, each pair of cross members 46 canbe elevated into position such that the two opposing cross members 46 ineach pair are separated by a flange portion 62 of the structural beam35. According to one embodiment, the first cross member 46 in theforward pair of cross members 46 can optionally be fixedly coupled tothe top rails 48 a, thereby preventing adjustment of the first crossmember 46 relative to the top rails 48 a in the forward and rearwarddirections. At least one, and optionally both of the cross members 46 inthe relatively rearward pair of cross members 46 can be adjustablycoupled to the top rails 48 a, allowing the rearward pair of crossmembers to be repositioned as needed for installation on a trailer 10having structural members 35 that are not equally, or conventionallyspaced. Once in position, the frame assembly 44, including the crossmembers 46, can be moved rearward (i.e., toward the aft portion 28 ofthe trailer 10) in the direction of arrows 66 in FIG. 7 a until theflange portion 62 is received within the recess 52 defined between thecross member 46 and the catch portion 50. With the flange portion 62received within the recess 52, the clamp 56 is pivoted in the directionof arrow 68 to contact the flange portion 70 of the structural beam 35.The locking nut 58 is then threaded onto the threaded member 64 untilit, or another intermediate structure such as a washer for example,makes contact with the clamp 56. Once the lock nut 58 is tight, as shownin FIG. 7 b, the clamp 56 prevents forward movement of the cross members46 relative to the structural beam 35 as required for removal of theframe assembly 44 from the trailer 10.

The position of the cross members 46 can optionally be made adjustablerelative to each other, or relative to another portion of the frameassembly 44. Adjustment of one or more of the cross members 46 forwardand/or rearward allow the frame assembly 44 to be coupled to trailers 10having different configurations. For example, suitable adjustment of thecross members 46 can be provided to allow the frame assembly 44 to becoupled to trailers 10 having structural beam 35 spacing from about 7inches to about 15 inches, on center.

The frame assembly 44 can optionally be coupled to the skirts 22 to besupported adjacent to each lateral side of the trailer 10 before theframe assembly 44 is coupled to the underside of the trailer 10.According to such an embodiment, the entire air drag reduction system 20can optionally be installed and removed as a unit. Thus, the air dragreduction system 20 can optionally be removed from one trailer 10 andinstalled on a different trailer quickly and efficiently. Fleetoperators would not be required to permanently install an air dragreduction system 20 onto each individual trailer, but would be able toquickly move the air drag reduction system 20 from one trailer 10 toanother.

FIG. 4 shows an illustrative embodiment of an intermodal trailer 80 thatis adapted to receive stackable shipping containers from one mode oftransportation (e.g., freighter, train, etc. . . . ) to be towed overpublic roads to be delivered to their destination. The intermodaltrailer 80 includes one or more, or optionally a plurality of structuralbeams 82 that extend longitudinally along the longitudinal axis 30.Unlike the trailer 10 described above, the intermodal trailer 80 lacksthe transverse structural members 35 that extend in a widthwisedirection across the trailer 10. Instead, the intermodal trailer 80includes a forward beam 84 at a leading end 86 and a rearward beam 88extending laterally across an aft end 90 of the intermodal trailer 80. Areceiver 92 is provided to each end of both the forward and rearwardbeams 84, 88. Each receiver 92 receives a corner of the shippingcontainer lowered into place by a crane, and locks the shippingcontainer in place until released at a time when the shipping containeris to be removed from the intermodal trailer 80.

To couple the frame assembly 44 to the intermodal trailer 80 in theabsence of the structural beams 35 discussed above, one embodiment ofthe frame assembly 44 includes cross members 94 that extend betweenrails 48 that support the skirts 96. Rather than suspending the crossmembers 94 from the underside of the intermodal trailer 80, the crossmembers 94 are adapted to rest on top of the structural beams 82extending longitudinally along the axis 30, as shown in the bottom viewof FIG. 4 and the cross-sectional view of FIG. 5, taken along line 5-5in FIG. 4. The cross members 94 can optionally include a clamp or otherfastening mechanism to secure the frame assembly 44 in place, the crossmembers 94 can optionally be urged against the structural beams 82 bythe force of gravity, the cross members 94 can optionally be maintainedin place between the structural beams 82 and a shipping containersupported by the intermodal trailer 80, any combination thereof, and thelike.

FIG. 6 shows an alternate embodiment of a cross member 100 suspendedfrom the structural beams 82 along an underside of the intermodaltrailer 80. The embodiment shown in FIG. 6 is a permanent installation,as opposed to the removable installation shown in FIGS. 4 and 5. In FIG.6, a central portion of the cross member 100 is releasably-coupled to anunderside of each of the structural beams 82 using a fastening system101 similar to that described above with reference to FIGS. 7 a and 7 b.Briefly, catch portions 105 are elevated up to, and slid over a flangeportion 107 of each of the structural beams 82 by moving the crossmember 100 in the direction of arrow 109 for the embodiment in FIG. 6.Once the catch portions 105 are properly positioned over the flangeportions 107, a clamp 111 and locking device 121 are secured over theopposite flange portions 125, thereby securing the cross member 100 inplace. Elevated arm portions 104 are approximately equal in elevation tothe top of the structural beams 82. Gussets 106 brace the elevated armportions, which cooperate with the rails 48 discussed below to supportthe skirts 96 adjacent to the lateral sides of the intermodal trailer80.

FIG. 8 shows an illustrative embodiment of a skirt segment 110 that canbe coupled adjacent to an end of the cross members 46, 94 to, along withadditional skirt segments 110, collectively form the skirts 22, 96. Eachskirt segment 110 is coupled to at least a top rail 48 a of the frameassembly 44. The top rail 48 a can be formed from 1 inch square metaltubing, and is supported adjacent to the end of the cross members 46,and can have an arcuate region, or be generally arcuate in shape overits entire length to establish the desired radius of curvature of thematerial forming the air deflecting surface while that material iscoupled to the top rail 48 a and/or bottom rail 48 b as describedherein. Other embodiments of the top rail 48 a can be formed from anysuitably-rigid material, in any desired cross-sectional shape tomaintain the shape of an arcuate region of the skirt when coupled to thetop rail 48 a. The embodiment of the skirt segment 110 shown in FIG. 8can be releasably coupled to the underside of the trailer 10 with asuitable fastening system, such as that described with reference toFIGS. 7 a and 7 b, provided directly to the top rail 48 a instead of thecross members 46. As such, the top rail 48 a is provided with aplurality of apertures 112 for receiving a catch portion 50 and lockingdevice 60 at a plurality of locations along the top rail 48 a toaccommodate trailers 10 with different structural beam 35 spacing. Thecatch portion 50 and locking device 60 can be at least partiallyreceived within the apertures 112 to be aligned with the desiredstructural beam 35 to be used to secure the skirt segment 110 to thestructural beams 35 of the trailer 10. By forming a plurality ofapertures 112 in the top rail 48 a, such as at one (1) inch intervals orother suitable spacing, the top rail 48 a can be made compatible with aplurality of differently-configured trailers.

The embodiment shown in FIG. 8 also includes a bottom rail 48 b. Thebottom rail 48 b, like the top rail 48 a, can be formed from squaremetal tubing, but can optionally be formed with smaller dimensions tosave on material costs. For instance, the bottom rail 48 b canoptionally be formed from ¾ inch metal tubing. Like the top rail 48 a,alternate embodiments of the bottom rail 48 b can formed from anysuitably-rigid material that will maintain its arcuate shape and providestructural support to a mid region of the skirt segment 110 to which itis coupled. Thus, while the truck 7 is underway, the structural supportprovided by the bottom rail 48 b to the mid region of the skirt segment110 is sufficient to allow the skirt segment 110, as a whole, towithstand the force imparted thereon by the airflow being deflected andmaintain its arcuate shape. The bottom rail 48 b can be elevated aheight H from the lowermost, or bottom region 49 of the material formingthe air deflecting surface of the skirt segment 110. Thus, the bottomrail 48 b is disposed at a vertical elevation, while the skirt segment110 is installed on the trailer 10, at a mid region of the materialforming the air-deflecting surface of the skirt segment 110 between thetop rail 48 and the bottom region 49. The height H can be chosen as anyvalue that provides adequate support to the bottom region 49 of thematerial forming the air-deflecting surface of the skirt segment 110,and prevents the bottom region 49 from bending inward, under the trailer10 to an extent that the bottom region 49 approaches an orientationparallel with the road surface (or underside of the trailer 10).Although minimal bending of the bottom region 49 is tolerable, theheight H can be chosen to allow the material forming the air-deflectingsurface of the skirt segment 110 to maintain substantially the sameshape as when not exposed to the airflow being deflected, andsubstantially-vertical orientation when subjected to the airflow beingdeflected while the truck 7 is underway, even at highway speeds. Inother words, the height H can be chosen such that the shape of thematerial forming the air-deflecting surface of the skirt segment 110 issubstantially the same when the truck 7 is underway as when the truck isstationary. For example, the height H can be any value such asapproximately half the vertical height of the material forming theair-deflecting surface of the skirt segment 110. According to alternateembodiments, the height H can be at least ten (10 in.) inches, or atleast twelve (12 in.) inches, or at least sixteen (16 in.) inches, or atleast twenty (20 in.) inches. Elevating the bottom rail 48 b in thismanner allows the bottom region 49 to deform if the bottom region 49makes contact with a foreign object such as the road surface, railroadtracks over which the truck 7 is traveling, or other object, forexample, without permanently deforming the material forming theair-deflecting surface of the skirt segment 110 or otherwise damagingthe air drag reduction system 20.

The bottom rail 48 b is supported by a brace 116 that extends at anapproximate 45° or other suitable angle from horizontal to thestructural beam 35, to which it is coupled using a reversible beamclamp, and the like. The length of the brace 116 can be selected alongwith the angle from horizontal to position a connector portion 51 thatis to be coupled to the beam 35 at approximately the same verticalelevation as an upper surface 55 of the top rail 48 a. The embodiment ofthe skirt segment 110 shown in FIG. 8 includes a single brace 116extending from the bottom rail 48 b, but alternate embodiments caninclude a plurality of braces 116 extending from the bottom rail 48 b ofat least one, or optionally each skirt segment 110. Yet otherembodiments can include a different number of braces 116 extending fromthe bottom rail 48 b of a plurality of different skirt segments 110included in a skirt 22. The brace 116 and bottom rail 48 b combinationprovide rigidity to a lower region of the skirt segment 110 that resistsforces imparted thereon by the airflow while the truck 7 is underway.The brace 116 can optionally be formed of a substantially rigid metal,metal alloy, plastic or synthetic composition, or a combination thereof.The brace 116 can be formed of a material having suitable rigidity andstrength to prevent, or at least minimize deflection of the brace 116,even when the lower region 49 of the material forming the air-deflectingsurface of the skirt segment 110 makes contact with a foreign object.The brace 116 can optionally be formed to have a cross-sectional shapethat is substantially I, H or L shaped to further resist bending orother deflection of the brace 116. Instead of damaging the brace 116,such contact between the lower region 49 and the foreign object causesthe lower region 49 to substantially-elastically deform to avoiddamaging the rest of the air drag reduction system 20. For embodimentswhere the skirt 22 is formed from a plurality of skirt segments 110,damage to any of the skirt segments 110 can be addressed by replacingonly the damaged skirt segments 110, but leaving the undamaged skirtsegments 110.

FIG. 9 shows an alternate embodiment of the skirt segment 110. As shown,the skirt segment 110 includes a plurality of elongated, and optionallyovular-shaped apertures 118 that are to receive a post 120, bolt orother suitable member extending from the top and/or bottom rail 48 a, 48b, shown using hidden lines in FIG. 9. Each post 120 can include anenlarged head that does not fit through the aperture 118 through whichthe post 120 extends. The end of the post 120 extending through theaperture 118 can cooperate with the top and/or bottom rail 48 a, 48 b,and optionally a compatible fastener such as a nut, pin, head or thelike, to interfere with removal of the post 120 from the aperture 118.The dimensions of the apertures 118 are suitable to permit relativemovement of the skirt segment 110 relative to the posts 120 in alongitudinal direction of the apertures 118, thereby allowing thematerial forming the air-deflecting surface of the skirt segment 110 tomove relative to the top and/or bottom rails 48 a, 48 b. Allowingmovement of the skirt segment 110 relative to the top and/or bottomrails 48 a, 48 b in the longitudinal direction enables materialssusceptible to high levels of thermal expansion to be used for the skirtsegments 110 without causing such materials to warp or otherwise deformto the extent that would occur if the skirt segments 110 were fixedlysecured to the top and/or bottom rails 48 a, 48 b. For example,materials such as ultra-high-molecular-weight polyethylene (e.g., havinga molecular weight within a range of approximately 2 million toapproximately 6 million) can be used as the material forming anair-deflecting surface of the skirt segments 110 despite thesusceptibility of that material to thermal expansion. Anultra-high-molecular-weight polyethylene air-deflecting surface is anexample of a material available for use due to the presence of theapertures 118 without the consequences resulting from thermal expansionthat may result from a fixed connection between the material forming theair-deflecting surface and the rails 48 a, 48 b. According to otherembodiments, the apertures 118 can allow the use of a combination ofmaterials having a substantial difference between their respectivecoefficients of linear thermal expansion (α). For instance, the rails 48a, 48 b can optionally be formed from aluminum, having a coefficient (α)of approximately 12.3×10⁻⁶ in./(in.×° F.), and the skirt materialcoupled to the rails 48 a, 48 b can optionally be formed from polyvinylchloride, which has a coefficient (α) of approximately 28×10⁻⁶in./(in.×° F.). Generally, the coefficient of linear thermal expansion(α) of one of the material coupled to the rails 48 a, 48 b and the rails48 a, 48 b themselves is at least about one and a half (1.5×) times(i.e., at least 150%) the coefficient of linear thermal expansion (α) ofthe other. In other words, the coefficient of linear thermal expansion(α) of the material coupled to the rails 48 a, 48 b can be at least oneand a half (1.5×) times, or 150% greater than the coefficient of linearthermal expansion (α) of the rails 48 a, 48 b, or vice versa.

The apertures 118 are elongated substantially parallel with a length(e.g., the longer dimension) of the material forming the air deflectingsurface of the skirt segment 110 because the length of the material inthis direction can result in substantial expansion and/or contractionrelative to any such expansion and/or contraction that occurs in theheight direction (e.g., vertical in FIGS. 8 and 9). The apertures 118can be sufficiently long to accommodate a full range of expansion and/orcontraction differences between the material forming an air-deflectingsurface of the skirt segments 110 relative to the rails 48 a, 48 b orother frame structure to which the material is coupled, optionally overa range of temperatures in which the air drag reduction system 20 isexpected to be used. For instance, the apertures 118 can be suitablylong to accommodate expansion and/or contraction differences over atemperature range from about −100° F. to about 140° F.

According to alternate embodiments, instead of forming elongatedapertures 118 in the material forming the air-deflecting surface of theskirt segments 110 and extending a post there through, a plurality ofposts can be fixed to, and project from fixed locations on the materialforming the air-deflecting surface of the skirt segments 110. Such postscan optionally extend through an elongated aperture formed in the topand or bottom rails 48 a, 48 b. Just as for the previous embodiment,thermal expansion and contraction of the material forming theair-deflecting surface of the skirt segments 110 causes the posts totravel along the length of the elongated apertures, thereby avoidingwarping of the material that would otherwise occur if the material wasfixedly connected to the rails 48 a, 48 b.

The skirt segments 110 in FIGS. 8 and 9 can have dimensions that allowskirt segments 110, all of the same dimensions, to be assembled tocollectively form different-sizes of skirts 22, 96. For example, theskirt segment 110 can be approximately 4 ft. in length. As shown in FIG.3, five skirt segments 110 are assembled to form the skirts 22 having alength of approximately 20 ft., which is suitable for use on a 53 ft.trailer 10. Likewise, FIG. 4 shows four skirt segments 110 arrangedtogether to form a skirt 96 having a length of approximately 16 ft.,which is suitable for use with the alternate trailer 80, which is lessthan 53 ft. in length, appearing in FIG. 4.

The skirt segments 110 can be joined together according to any suitabletechnique. An illustrative embodiment of a connector for joining skirtsegments 110 is shown in FIGS. 13 and 14. In FIG. 13, a portion of aplurality of skirt segments 110 a, 110 b (FIG. 14), viewed on end inFIG. 13, extend into a substantially C-shaped recess defined by aC-channel clamp 115. A fastener 117 (partially shown in hidden lines)such as a rivot, screw, bolt, etc. . . . extends through both the clamp115 and the skirt segments 110 a, 110 b, thereby interfering withremoval of the skirt segments 110 a, 110 b from the clamp 115. However,it is understood that any suitable device for joining two or more skirtsegments 110 together can be used without departing from the scope ofthe present invention.

An alternate embodiment for joining skirt segments 110 is illustrated inFIGS. 15 and 16. According to such an embodiment, a joining section 114of square tube that can be at least partially received with in thesquare tube of the top rail 48 a is provided with a pair of apertures135 formed therein. For instance, the top rail 48 a of each skirtsegment 110 can be formed from 1 inch square tube, and the joiningsection 114 can be formed from ¾ inch square tube. The ends of the toprail 48 a of each skirt segment 110 to be joined are placed over thejoining section 114 such that apertures 137 in each top rail 48 a arealigned with the apertures 135 in the joining section 114, as shown inFIG. 16. A pin, bolt or other suitable fastener can be inserted throughthe aligned apertures 135, 137 to couple the top rails 48 a together.

Forming skirts 22, 96 from a plurality of modular skirt segments 110 asshown in FIGS. 3 and 4 also allows for replacement of a damaged skirtsegment 110, rather than replacement of an entire skirt 22, 96.Replacement of individual skirt segments 110 instead of the entireskirts 22, 96 is cost efficient and allows for quick repairs compared toremoving and replacing the entire skirts 22, 96.

The material selected for the skirt segments 110 can optionally beblended with the color of choice, or otherwise incorporate the color ofchoice throughout. When the material used for the skirt segments 110 isscratched or otherwise damaged, the color of choice is still visible andthe damage does not stand out like it would if the color of choice wasmerely a surface coat and was damaged to reveal a different colorunderneath.

The material used for the skirt segments 110 can also optionally includea mark indicative of a quality of the skirts 22, 96, the skirt segments110, or a combination thereof. For example, the mark can be acertification mark indicating that the skirts 22, 96 have been testedand were found to improve fuel economy by a predetermined percentage ona test vehicle. The mark can optionally be indelibly provided to theskirt segment 110. For example, the mark can be integrally molded aspart of the skirt segment 110 itself. According to alternateembodiments, the mark can optionally be impressed, branded or otherwisepermanently formed in or on the skirt segments 110.

FIGS. 10 a, 10 b and 10 c are cross-sectional views of the skirt segment110 taken along line 10-10 in FIG. 9. The cross section shown in FIG. 10a includes a rib 130 molded lengthwise along the skirt segment 110. Therib 130 provides the skirt segment 110 with enhanced rigidity andsupport, possibly allowing for omission of the brace 116 that offerssupport to the bottom of the skirt segment 110.

The cross sections shown in FIGS. 10 b and 10 c each include a region132 of added material thickness and a region 134 of lesser materialthickness. In FIG. 10 b, the region 132 with added thickness offersenhanced rigidity and durability to the bottom portion of the skirtsegment 110. Since the top rail 48 a offers sufficient support adjacentto the top of the skirt segment 110, there is less need for the addedmaterial thickness in the region 134 adjacent to the top of the skirtsegment 110. Likewise, for embodiments where there is less need for theadded rigidity and support adjacent to the bottom of the skirt segment,the region 134 of lesser material thickness can be so located, as shownin FIG. 10 c. Minimizing material thickness reduces material consumptionand offers potential cost savings.

FIG. 11 illustrates positioning of the air drag reduction system 20 onthe underside of a trailer 140, with the structural beams 35 removed forclarity. For any of the embodiments described herein, the skirt 142 canoptionally include a region 144 adjacent to a trailing end 146 of theskirt 142 that is substantially parallel with the side 148 of thetrailer 140, the axis 30, or both. By allowing the curvature of theskirt 142 to reach an end in parallel with the axis 30, side of thetrailer 148, or both, a substantially laminar deflected airflow 150 isbelieved to result. It is also believed that the substantially laminardeflected airflow 150 minimizes formation of turbulent eddies 152 (FIG.12) adjacent to the aft portion 28 of the trailer 140. In contrast, itis believed that the deflected airflow 160 produced by anon-substantially-parallel skirt 162 as shown in FIG. 12 promotesformation of such turbulent eddies 152, and projects water from the roadsurface into the path of auto traffic.

Illustrative embodiments have been described, hereinabove. It will beapparent to those skilled in the art that the above devices and methodsmay incorporate changes and modifications without departing from thegeneral scope of this invention. It is intended to include all suchmodifications and alterations within the scope of the present invention.Furthermore, to the extent that the term “includes” is used herein, suchterm is intended to be inclusive in a manner similar to the term“comprising” as “comprising” is interpreted when employed as atransitional word in a claim.

What is claimed is:
 1. An aerodynamic drag reduction apparatus forreducing aerodynamic drag on an over-the-road vehicle while underway,the aerodynamic drag reduction system comprising: a frame assembly thatis adapted to cooperate with a cargo-carrying portion of theover-the-road vehicle to couple the drag reduction apparatus to theover-the-road vehicle; a first skirt adapted to be supported beneath afirst lateral side of the cargo-carrying portion of the over-the-roadvehicle; a first upper rail that is to be coupled adjacent to an upperregion of the first skirt to extend longitudinally along the first skirtand provide the first skirt with an arcuate region between a forwardregion and a trailing region of the first skirt; a first lower rail thatis to be coupled to the first skirt at a vertical elevation between thefirst upper rail and a bottom region of the first skirt to extendlongitudinally along the first skirt; a second skirt adapted to besupported beneath a second lateral side, opposite the first lateralside, of the cargo-carrying portion of the over-the-road vehicle; asecond upper rail that is to be coupled adjacent to an upper region ofthe second skirt to extend longitudinally along the second skirt andprovide the second skirt with an arcuate region between a forward regionand a trailing region of the second skirt; and a second lower rail thatis to be coupled to the second skirt at a vertical elevation between thesecond upper rail and a bottom region of the second skirt to extendlongitudinally along the second skirt.
 2. The aerodynamic drag reductionapparatus of claim 1 further comprising: a first brace that extendsbetween the first lower rail and an underside of the cargo-carryingportion when the aerodynamic drag reduction apparatus is installed; anda second brace that extends between the second lower rail and theunderside of the cargo-carrying portion when the aerodynamic dragreduction apparatus is installed.
 3. The aerodynamic drag reductionapparatus of claim 1, wherein the first and second upper rails and thefirst and second lower rails comprise an arcuate shape, having a radiusof curvature of at least 12 inches.
 4. The aerodynamic drag reductionapparatus of claim 1, wherein the first and second skirts each comprisea plurality of equal-length skirt segments coupled together.
 5. Theaerodynamic drag reduction apparatus of claim 4, wherein each of thefirst and second upper rails and each of the first and second lowerrails are formed from a plurality of rail segments coupled together, andeach of the skirt segments comprises an upper rail segment and a lowerrail segment.
 6. The aerodynamic drag reduction apparatus of claim 1,wherein the frame assembly comprises a cross member extending betweenthe first and second skirts, the cross member comprising a connector forcoupling the aerodynamic drag reduction apparatus to the cargo-carryingportion of the truck.
 7. The aerodynamic drag reduction apparatus ofclaim 6, wherein the connector comprises an adjustable clamp forreleasably coupling the frame assembly to the cargo-carrying portion ofthe truck.
 8. The aerodynamic drag reduction apparatus of claim 1,wherein each of the first and second skirts is approximately 20 ft.long.
 9. The aerodynamic drag reduction apparatus of claim 1, whereineach of the first and second skirts is approximately 16 ft. long.
 10. Anaerodynamic drag reduction apparatus for reducing aerodynamic drag on anover-the-road vehicle while underway, the aerodynamic drag reductionsystem comprising: a frame assembly that is adapted to cooperate with acargo-carrying portion of the over-the-road vehicle to couple the dragreduction apparatus to the over-the-road vehicle; a first skirt adaptedto be supported beneath a first lateral side of the cargo-carryingportion of the over-the-road vehicle; a second skirt adapted to besupported beneath a second lateral side, opposite the first lateralside, of the cargo-carrying portion of the over-the-road vehicle,establishing a space separating a leading portion of the first andsecond skirts; and a coupling system that is to couple the first andsecond skirts to the frame assembly in a manner that allows thermalexpansion and contraction of the first and second skirts relative to theframe assembly without warping of material forming an air-deflectingsurface of the first and second skirts to an extent that would occur ifthe first and second skirts were fixedly connected to the frameassembly.
 11. The aerodynamic drag reduction apparatus of claim 10,wherein the coupling system comprises: a plurality of elongatedapertures formed in the material forming the air-deflecting surface ofthe first and second skirts; and a post that extends through each of theplurality of elongated apertures and at least partially through aportion of the frame assembly to allow longitudinal adjustment of thematerial forming the air-deflecting surface relative to the frameassembly.
 12. The aerodynamic drag reduction apparatus of claim 10,wherein: the first skirt comprises a plurality of first skirt segmentsthat are arranged to collectively form the first skirt, and each of thefirst skirt segments comprise a plurality of elongated apertures formedin the material forming the air-deflecting surface of the first skirt;the second skirt comprises a plurality of second skirt segments that arearranged to collectively form the second skirt, and each of the secondskirt segments comprise a plurality of elongated apertures formed in thematerial forming the air-deflecting surface of the second skirt; and thecoupling system comprises a post that extends through each of theplurality of elongated apertures and at least partially through aportion of the frame assembly to allow longitudinal adjustment of thematerial forming the air-deflecting surface of the first and secondskirt portions relative to the frame assembly.
 13. The aerodynamic dragreduction apparatus of claim 10, wherein the material forming theair-deflecting surface of the first and second skirts comprisespolyethylene with a molecular weight within a range of approximately 2million to approximately 6 million.
 14. The aerodynamic drag reductionapparatus of claim 10, wherein each of the first and second skirtscomprises an arcuate region comprising a radius of curvature of at least12 inches.
 15. The aerodynamic drag reduction apparatus of claim 10,wherein each of the first and second skirts comprises a length within arange from approximately 15 ft. to approximately 21 ft.